(1) Field of the Invention
The present invention relates to a CAD (computer-aided design) system for generating a graphic drawing by placing figures corresponding to objects on a display screen, and more particularly to a CAD system for generating graphic drawings of buildings or the like.
(2) Description of the Related Art
CAD systems for use generating graphic drawings of buildings handle columns, walls, fittings, etc. as objects, and generate graphic drawings of buildings by placing figures representing those objects in desired positions on a display screen. It is a general practice to indicate the positions where the figures are to be placed with a pointing device such as a mouse or the like.
For placing a figure on the display screen, it may occasionally be necessary to establish detailed settings. For example, such detailed setting are required when a wall is to be positioned between columns so that surfaces of the wall and the columns lie flush with each other. To position the wall between the columns on the display screen, sides of figures representing the columns and a side of a figure representing the wall have to be aligned with each other. According to one simple process, a desired position for the wall may be indicated by a pointing device such as a mouse through fine adjustment of the pointing device. This process, however, is disadvantageous in that it is difficult for the user to control the pointing device for fine adjustment, and it is time-consuming to indicate the desired position.
Some conventional CAD systems are capable of indicating a desired position of a figure by entering a command from a keyboard in a command entry mode. When a wall surface distance for a figure is established by entering a numerical value, the position where the figure is to be placed deviates from a reference point depending on the established wall surface distance. By setting a suitable value to the wall surface distance, it is possible to bring the position where the figure is to be placed into a desired position. Therefore, sides of figures representing the columns and a side of a figure representing the wall can be aligned with each other by setting a suitable value to a wall surface distance.
For generating a graphic drawing for a building, it is necessary to follow certain layout rules which are peculiar to the building drawings. For example, a fitting has to be placed on a wall or the like. Consequently, designers who produce design drawings for buildings are required to indicate positions where figures are to be placed with those layout rules in mind.
For a CAD system user to indicate various parameters including the wall surface distance from command lines, the user has to be aware of the names and meanings of various parameters. Since the names of parameters are represented by simple strings of letters, the meanings of the parameters cannot be recognized based on the names thereof. Therefore, CAD systems cannot be fully operated by users unless they have a certain level of knowledge about the parameters.
Because of the layout rules peculiar to the building drawings, CAD system users must always understand what objects are represented by the figures displayed on the display screen and how they are related to an object which is going to be added. Furthermore, certain objects need their shapes to be established in addition to their positions. For example, when a door is to be placed in the graphic drawing on the display screen, it is necessary to establish the direction in which the door can be opened in addition to the position where the door is to be placed. As a result, the conventional CAD systems for generating graphic drawings for buildings have posed an excessive burden on building designers who use those CAD systems to generate building design drawings.